Electron paramagnetic resonance studies and linewidth anomaly of Cr³⁺ in some ferroelectric alums

Abstract

Electron paramagnetic resonance of Cr³⁺ in CH₃NH₃Ga(SO₄)₂.12H₂O and CH₃NH₃Al(SeO₄)₂.12H₂O (which are known to be ferroelectric) as a function of temperature and orientation has been studied. As one approaches T_c, an anomalous increase of resonance linewidth, which is very pronounced for the satellite transitions has been observed. It is observed experimentally that ΔH_C~( T-T_C)^-n, where n~ 0.4 for temperature near to T_c and n~2.0 for temperatures further from T_c. The EPR spectrum has also been observed in the ferroelectric phase. It is inferred that the water molecules in the immediate environment of the trivalent metal ion may be playing an important role in the mechanism of ferroelectricity in alums.